purpose is shown in Fig. 87, which is merely a small and narrow,
graduated cylinder holding 10 c.c.1 The solubility of a portion
of the liquid is an indication of the presence of a
mixture. Furthermore, the specific gravity of the in- A
soluble portion (its floating or sinking in the water) *&
will be roughly indicated and should be noted.
A Solid.—If the substance is a solid, examine a
few particles on a slide under the microscope, or,
better still, recrystallise a little if possible and notice
if the crystals appear similar in shape. If it is a
mixture, try to separate the constituents by making a
few trials with different solvents, water, alcohol, ether,
benzene, petroleum spirit, ethyl acetate, acetic acid, etc.
If it appears homogeneous, determine the melting-
point, the sharpness of which will be a further con-
firmation. If it turns out to be a mixture, it must
be further treated in the manner described under
" mixtures " (p. 343).
The Action of Heat.—We will assume in the first
place that the substance is homogeneous and consists
of a single individual. Heat a portion on platinum foil and
notice if it volatilises, chars, or burns with a clear, luminous,
non-luminous (aliphatic), or smoky (aromatic) flame. Determine
the nature of the residue, if any? when the carbon has burnt
Metalor metallic oxide or carbonate may indicate the presence
of an organic acid, phenate, or double salt of a base.
Sulphate^ sulphite, or sulphide may indicate a sulphate,
sulphonate, mercaptan, or bisulphite compound of an aldehyde
Cyanide may indicate a cyanide or ferrocyanicle, etc.
Heat a little of the substance in a small, hard-glass tube and
observe whether the substance melts, chars, explodes, sublimes,
or volatilises ; whether an inflammable gas, water, etc., is evolved ;
also notice the smell.
Carbohydrates, polyhydric alcohols, higher organic acids (e.g.>
stearic), dibasic and hydroxy-acicls (^., tartaric), certain amides
(e.g.) oxamide), alkaloids, and azo and other organic colours char
1 Both pieces of apparatus (Figs. 86 and 87) can be obtained from Mr. O. Baum-
bach, %, Lime Grove, Oxford Street, Manchester.